Electrically powered motor vehicles typically carry batteries aboard for supplying operating power. These batteries must periodically be recharged. Recharging can be accomplished in a number of ways. The vehicle may be a purely electrically operated vehicle, so that operation is fully dependent upon charge remaining in the batteries. The batteries of such vehicles must be charged from an external power source, for example, the AC mains.
Alternatively, the vehicle may be a hybrid vehicle having an onboard internal combustion engine. The internal combustion engine may provide a portion of the traction energy, either alone, or in combination with the vehicle's electric motor. In most hybrid vehicles currently available, the internal combustion engine is solely responsible for keeping the vehicles on-board batteries charged.
A new generation of hybrid vehicles, the so-called “plug-in” hybrids may also be equipped for battery recharging from an external power source such as the AC mains.
Many electrically powered vehicles, whether hybrid or purely battery powered, may have a regenerative braking feature in which braking operates a dynamic brake, which also functions as a generator for recharging the batteries.
Regardless of the type of vehicle and of the particular operating scheme, in commercially available electrically operated vehicles both of the purely electrical type and also of the hybrid type, it may become necessary or desirable that the batteries be recharged enroute. Recharging of batteries of the type suitable for powering conventional passenger vehicles presents conflicting demands. On one hand, it is desirable to minimize the time interval during which the vehicle is being charged. However, it is also desirable to limit voltages present during charging due to safety and other concerns. Most electrically powered vehicles utilize a number of individual batteries series connected to achieve a high operating voltage to power the electric motor thereof. One popular, commercially available hybrid automobile uses 210 volts as an operating voltage.
It is possible to recharge the individual batteries at limited voltage. One approach to such recharging is to charge batteries in parallel at a relatively low voltage, and to then reconnect the batteries into a series configuration for supplying power to the vehicle at a higher voltage. There is however, an inverse relationship between the available charging time and the current that must be supplied to the individual batteries. In other words, the shorter the available charging time, the higher the current required to charge the individual, parallel-connected batteries.
Inductive couplings have been developed to facilitate ready battery recharging. However, inductive couplings introduce inefficiencies, notably, heating losses from induction. It is preferable to provide direct mechanical connection between charging conductors and those conductors leading to the batteries being charged to avoid inductive losses.
Batteries can be charged over long periods of time (i.e., trickle charged), for example overnight at the residence of the operator or all day at the operator's place of business. However, even the largest capacity contemporary batteries are limited as to the practical cruising range of their associated vehicles. For relatively short “out and back” trips such as commuting to a workplace, an overnight trickle charge may be sufficient to power the vehicle. However, for longer trips, it becomes very likely that many electric vehicles will have to be recharged while the operator is between a departure point and a destination.
High current recharging requires relatively large contacts for receiving charge current, large switches for making the transition between parallel and series battery connections, and relatively large conductors for serving the contacts and switches. Such large structures are required to carry the required charging currents while minimizing resistive losses.
Passenger vehicles are consumer items. That is, they are typically operated by laymen, or people who are not trained in the mechanics and electrical systems of passenger vehicles. It is, therefore, necessary that any system for recharging the batteries of electrically powered vehicles be simple to operate and include inherent safety features so that consumers can safely recharge their vehicles.
There exists a need for a practical way to arrange relatively expeditious, relatively safe recharging at commercial premises for operators of electrical vehicles.